package com.wc.fortnight_blue_bridge.Q231125.Q8735;

import java.util.Arrays;
import java.util.Scanner;

/**
 * @Author congege
 * @Description
 * @Date Created in 2023/11/25-22:30
 */
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] array = new int[3];
        int s = 0;
        for (int i = 0; i < 3; i++) {
            array[i] = sc.nextInt();
            s += array[i];
        }
        Arrays.sort(array);
        if (array[0] + array[1] <= array[2]) {
            System.out.println(-1);
            return;
        }
        s /= 2;
        int sum = s;
        for (int i = 0; i < 3; i++) {
            sum *= (s - array[i]);
        }
        System.out.println(sum);
    }
}
